Treatment of toluidine bases



Patented July 30, 1.935

Catlow, Oswaldtwistle, England, assignors to William Blythe & Company Limited, Holland Bank Chemical Works,

company England, a British No Drawing. Application July 20, 1931, Serial .No 552,064. In England August 12, 1930 11 Claims. (01. 2s0 1s0.5)

pound with the para-toluidine (i. e. 1 molecule for This invention relates to the treatment of toluidine bases. e

One object of the invention is to separate para-toluidinef from admixture with, ortho- 5 .toluidine. Another object is to ,form new compounds of ,para-toluidine with sulphur dioxide which are solid at ordinary temperaturesand can be used conveniently and effectively as a means for separating; para-toluidine from ad mixture with otherqsubstances especially analogou's or isomeric'bases such' as ortho-toluidine. -A further object .is to separate'into its 'com- Iponents .a mixture of orthoand para-toluidine such as'is obtained by direct reduction of the technical mono-nitration product of toluene. The productlobtained by this "direct reduction is a fluid mixture of toluidines consisting mainly of the orthoand para-isomers approximately in the proportion of 2 to 1 respectively. It is usually distilled from the reaction mixture with steam, thus becomingxsaturated with water.

Many methods have been proposed for the separation of the isomers from this mixtureand though these methods areon the whole successful they possess the disadvantage of being tedious on account of their incompleteness whereby the operations may need frequent repetitlon before complete separation is achieved. 7 Now we have found that wecan, separate paratoluidine from admixture with ortho-toluidine by treating the mixture with a limited quantity vof. sulphur dioxide preferably in the presence of a small proportion of water.- By this treatment a solid compound of 'para-toluidine, sulphur dioxide and wateris precipitated which can be separated by filtration and good pressing. In the. absence of water a solid compound of paratoluidine and sulphur dioxide is also obtainedbut the separation of the para-toluidine from the "mixture is very muchless complete when water is absent.

The composition .of the solid compound when water is'pres'ent corresponds approximately to the chemical formula .zcqnm, S04E20. The composition of the solid compoundwhen 'wateris not present corresponds approximately to; the formula' Y 2C7H9N, s02. V vIn using the expression limited quantity {we mean that the quality of sulphurdioxide employed,'although it may be larger thanthat theoretically necessary to form a double comphur dioxide and water. to be decided by the requirements of circumeach 2 molecules of para-toluidine) is verysubstantially lessthan would be necessary to combine with all the toluidines present. The proportionof water is kept as low as possible and need'not exceed one molecule'for each molecule of sulphur dioxide.

Crude :toluidine (containing about one third of its weight of para-toluidine) when saturated with water, for example after being submitted to steam distillation, contains about 5 to 6"per cent. of water and. we have found that this is a-suitable proportion for the production of the double compound of para-toluidinewith sulphur dioxide and water, although slightly larger than that indinecessary, but this is very much less than would be required to combine-with all the orthotoluidine present in the mixture.

'The successful separation probably depends upon the sparing solubility of the para-toluidine compound in ortho-toluidine at. the ordinary temperature. v j i When moderatelyj heated (80-1007 C.) preferably ;-under reduced pressure the double compounds part with their sulphur dioxide or sulphur dioxide and; water leaving practically pure paratoluidine which solidifies on cooling. 1 The oil from which the aforesaid solid compound of para-toluidine, sulphur dioxide and water has beenseparated approaches in composition the ortho-toluidine of commerce. It diffew from the latter in containing a little more para-toluidine as well as a small amount of sul- Its furthertreatment is stances. r I

If, for example, the oil is utiliz-able as such, the

.small quantity of sulphur dioxide and. water may beremoved if necessary bythe application of heat, preferably under reduced pressure, or alternatively the oil maybe washed with a small amount of caustic alkali.

If,.however, a technically pure ortho-toluidine base is required, then the oil may be mixed with about l0'per cent of its weight of fiftyper, cent sulphuric acid and distilled in steam. whereby technically pure ortho-toluidine .distills over and is collected. Alternatively if technically pure 'ortho-toluidine hydrochloride is required the oil may be mixed with a, slight" excess of a molecular proportion of 30 percent. hydrochloric acid, and. after thorough cooling of the mixture, the cryst-ain besides ortho-toluidine, the rsmall remainder of the para-toluidine originally present in the starting material (1. e. thecrude toluidine and these may be suitably treated with alkaligtoliberate the toluidine bases which can then be added to another batch of crude toluidine for further treatment with sulphur dioxide. If preferred,

the liberated toluidine bases may be treated sepa-"f rately.

It is known that crude toluidinesobtained by the mono-nitration of toluol and direct reduction of the product contains a small proportion of "meta-toluidine but no separation of this isomer-is effected by this invention and the small'proportion of meta-toluidine present in the original crude base remains, after the separation 'of-the para-toluidine, with the ortho-to'luidine'and is reckoned as such.

- In illustration of the manner by which we-may carry out our invention we quote the following -example:'-

Wet crude toluidineK'ZOO parts by weight) ob tainedby mono-nitration o'f toluol, subsequent reduction of the product and steam distillation and containing approxir'natel-y 32 per cent of para-toluidine and '5 to 6 per cent of water is allowed to absorb sulphur dioxide (95 parts by weight) preferably under agitation and without cooling below 80 C. After operation the oily liquid is cooled and thereby becomes semi-solid owing to the formation of the crystalline compound. The product is preferably cooled 'below 15 C. and then filter pressed as :dry as possible.

The press cake is after-wards placed in a jacketed pan'and warmed by hot water or steam in the jacket to a temperature of 80-100 C. This-causes an evolution of sulphur dioxide which is led away by a pipe andtutilized in a subsequent operation or in any other desired manner. 1

Towards the end of theevolution of the sulphur dioxide the removal of the-last portions 'of the sulphur dioxide may be assisted by reducing the pressure in the pan by means of a suction pump or by the passage of an inert gas through the molten mass. When the sulphur dioxide has ceased to be evolved the liquid contents of the pan consisting of para-toluid'ine base are run out or bailed out of the pan into moulds to cool and solidify.

If the evolution of sulphur dioxide in the last operation has been imperfect with the consequence that the para-toluidine base is contaminated with a little sulphur dioxide'ior with sulphate due to oxidation-by contact with air) the para-toluidine base may be purified by suitably washing it with dilute caustic alkali and afterwards with water and" then drying again.

When the operations havebeen properly carried out the melting point of the para-toluidine base is approximately 45 C. which is clear evidence of the purity of the product.

If, however, the operations have been imperfect and the melting'p'o'int of the para toIuidine is lower than is desirable it may be purified and its melting point thereby raised by; hydro-extraction or hydraulic pressing at suitably elevated temperatures approaching that of its melting point. The yield of the para-toluidine compound is approximately 270 parts and of para-toluidine base from the same 198 parts the yield being about 90 per cent. of that theoretically possible.

The oil from the aforementioned press cake as stated in the" introduction, is mainly orthotoluidine. It still contains about 4 per cent of para-toluidine and if circumstances demand the preparation .of technically pure ortho-toluidine base or hydro-chloride it may be treated in either of the ways described or by any other suitable known method.

.By either of the two methods mentioned a residual aqueous liquor remains containing in addition to drtho-toluidine the rest of the parato'luidine contained in'the original crude toluidine.

'This liquor is concentrated if necessary and treated with caustic soda or other alkaline agent in order to' liberate the mixed toluidine bases which are then suitably removed and added to more crude toluidine for further treatment with sulphur dioxide. If preferred, however, this residualoil may be kept apart and allowed to ac- 'cumulate until the quantity is large enough to be submitted separately -'to the'above described treat- -ment with sulphur dioxide. We declare that what we claim is:

- 1. Process for isolating para-'toluidine from admixture with ortho-toluidine which includes the step of 'itreating the'mixture with sulphur dioxide to bring about reaction between said paratoluidine and saidsulphur dioxide-and separating the solid compound formed by said reaction from the mixture. I 3

2. Process for isolating para-toluidine' from admixture with ortho-toluidine which includes the step of treating-the mixture with sulphur dioxide in presence of water to bring about reaction betweensaid para-toluidine. sulphur dioxide and water and separating the solid compound formed by'said reaction from the mixture.

3. Process for isolating para-toluidine from admixture with ortho-toluidine which includes the steps of treating the-mixture with a quantity of sulphur dioxide not substantially in excess of that required to combine with the para-toluidine. bringing about a reaction between said paratoluidine and said sulphur dioxide to form asolid compound therewith, and then separating said solid compound from the mixture.

' 4. Process for separating para-toluidine from admixture with ortho-toluidine which consists in treating the mixture with sulphur dioxide in presonce of water, the quantity of said sulphur dioxide and said Water being not substantially in excess of that required to combine with the paratoluidiiie, bringing about a reaction between said para-toluidine, sulphur dioxide and water to form a-solid compound, separating said solid compound from the mixture and then splitting off sulphur dioxide from said solid compound. l e

5. Process for separating para-toluidine from admixture with ortho-toluidine as claimed .in claim 4 in which the said solid compound is decomposed by heating to yield free toluidine.

6. Process for separating para-toluidine-from admixture with ortho-toluidine as claimed in claim 4 in which the said solid compound is separated from the mixture by filtration and is pressed to remove adherent ortho-toluidine.

"7. Proces's'for separating paratolu1dine from admixture'with ortho-toluidine which consists in treating the mixture with sulphur dioxide to'brin'g about reaction between said para-toluidine and said sulphur dioxide, separating the solid compound formed by said reaction from the reaction mixture by filtration and pressing and decomposing it to yield a base consisting mainly of para-toluidine.

8. Process for separating para-toluidine from admixture with ortho-toluidine which consists in treating the mixture with a quantity of sulphur dioxide not substantially in excess of that required to combine with the para-toluidine, bringing about a reaction between said para-toluidine and said sulphur dioxide to form a solid compound, separating said solid compound from the reaction mixture and decomposing said solid compound to yield a base consisting mainly of para-toluidine.

9. Process for separating para-toluidine from admixture with ortho-toluidine which consists in treating the mixture with a quantity of sulphur dioxide and water not substantially in excess of that required to combine with the para-toluidine, bringing about a reaction between said paratoluidine, sulphur dioxide and water to form a solid compound, separating said solid compound from the reaction mixture and decomposing said dioxide not substantially in excess of that required to combine with the para-toluidine, bringing about a reaction between said para-toluidine and said sulphur dioxide to form a solid compound, and then separating the solid compound 7 so formed from the reaction mixture anddecomposing it to liberate para-toluidine.

11. Process for isolating para-toluidine from admixture with ortho-toluidine which includes the steps of treating the mixture with a quantity of sulphur dioxide and water not substantially in excess of that required to combine with the paratoluidine, bringing about a'reaction between said para-toluidine, sulphur dioxide and water to form a solid compound and then separating the solid 20 compound so formed from the reaction mixture.

WILLIAM HENRY BENTLEY. BENJAMIN CA'I'LOW. 

